Old Question but here you go- 3 fans are always better doesn't matter if the size of the fans is small as heat sink will be larger, they run more silently too (it depends from card to card tho). I don't own it but I know that INNO3d 3 fan or 4 fan cards run extremely silent.

Again it will vary a lot from brand to brand and card to card. I have 12 card rig of same brand and I can see 10-12C difference between some of my cards.

You can't go wrong with tier-1 brands like Sapphire. Sapphire pulse RX 570 2 fan will run at low temp then PowerColor RX 570 3 fan.